The invention relates to an apparatus for electrolytic surface coating of pourable material, preferably for electrodeposition of metal, in particular aluminum, from an electrolyte. The pourable material is transported in the cathodic track of a vibrator conveyor at least partly in the treatment bath of the electrolyte.
It is known that by surface improvement of metal parts their life can be lengthened and new areas of use can be opened up. For example, the coating of light metal and ferrous materials may be appropriate, as they generally involve relatively base metals, the surfaces of which may corrode under atmospheric action. Suitable pretreatment gives the parts a polished surface without cover layer. The metallic coating may be supplemented with an aftertreatment.
During the electrodeposition the pourable small parts must be held together so that each individual part has electric contact. On the other hand, the bulk material to be treated should be spread out to the extent that the metal deposition can occur on a product surface as large as possible and a current density as uniform as possible is ensured on all parts. Another essential prerequisite for satisfactory metal coatings with a uniform layer thickness is sufficient mixing of the material during the electrodeposition. The apparatus for electrolytic surface coating is equipped with conveying means for the transport of the bulk material through the electrolyte, which in conjunction with corresponding inlet and outlet locks permit either continuous or intermittent feeding and removal of the material. In addition, the movement through the electrolyte and the thorough mixing of the material as well as the transport through the electrolyte must be carried out in such a way that gentle treatment of the material is ensured and even delicate parts are not mechanically damaged during the electrodeposition.
For mass electrodeposition, in particular for electrodeposition of aluminum, a known apparatus is suitable in which a vibrator conveyor with a horizontal and a vertical vibration component is provided for the transport of the pourable material through the treatment bath. This vibrator conveyor transports the pourable material, utilizing the forces of gravity, in a spiral conveying trough in ascending direction around a central pipe connected with the conveying trough. The vibrator conveyor is accommodated with the central pipe in a gasproof vessel which contains an electrolyte into which the vibrator conveyor dips partially. As drive means are used for example oblique-action vibrators or obliquely set rods. Such vibrator conveyers require relatively little drive force and make possible a gentle conveyance of the pourable material. One obtains intensive product movement and good electrolyte exchange as well as uniform current consumption over the entire effective surface of the spread-out material (EP-A0 209 015).
In a known apparatus for the plating of parts by immersion and movement in a plating solution, these parts execute a vibrational movement and at the same time a circular movement. The parts are present with the plating solution in a vessel. The movement path of the parts leads from a lower entry zone spirally upward to an exit zone. For moving the parts, the entire vessel containing the plating solution is made to vibrate (FR-A 2 103 611).
Since during the coating the material of the anodes is eroded and deposited on the bulk material, the anodes must, as is known, be replaced after a predetermined number of hours of operation. Further it is desired to obtain a high material utilization of the anodes, and in addition the availability of the installation is to be maintained by reduction of the down times for changing the anodes.
For the electrolytic surface coating of pourable material, in particular for the electrodeposition of aluminum in a vibrator conveyor system, the anodes may be disposed, accessible from the outside, on the inner wall of the vessel or on a so-called anode shaft cover. As the anodes are used up by the coating process, their life is limited to a predetermined number of hours of operation. For this reason they are replaced when about 50 to 70% of their material has been used up. This is necessary because otherwise the anodes may corrode through if the erosion is irregular and the remaining stumps may warp due to their dead weight and may thus establish a shortcircuit to the cathode. For changing the anodes, the installation filled with electrolyte at about 100.degree. C. must be cooled, emptied, flushed with toluene, and dried. The electric leads of the anodes are disconnected, the anodes exchanged through openings in the vessel wall, and for restarting the apparatus these operations occur in reverse order.